No, he didn't! () Christopher was involved with the production; he sent the scriptwriters tapes of how to pronounce Tolkien's words and names. The BBC made a typescript of this - the Tolkien Society had a few copies for sale way back when; I bought one.

Interestingly enough, CT reckoned Thengel ought to have been pronounced 'Thenjel' - then changed his mind: 'Thenjel' is correct in Old English, but not in Middle-earth.